Damp Behind Bathroom Tiles - Why It Happens and What a Real Fix Costs

Tap testing across the tiled area: a hollow, dull note over a patch rather than a single tile suggests the board behind has softened.

A pinless moisture meter gives a comparative reading between the shower wall and a dry wall in the same room. Absolute numbers matter less than the difference.

Smell and staining at skirting level in the adjoining room often confirm it without touching the bathroom at all.

Strip the affected tiles plus a generous margin, remove any saturated plasterboard, and let the timbers dry - plasterboard in a wet zone should not be re-covered while damp.

Re-board with a tile backer board rather than moisture-resistant plasterboard in the shower zone. Backer board does not soften when it eventually gets wet.

Apply a liquid tanking membrane with reinforcing tape at every corner and pipe penetration, then tile onto that. This is the layer that stops it happening again.

Replacing three tiles onto a board that is still wet, with no membrane behind, gets you the same phone call next year. If the wall is opened, it is worth doing the build-up correctly while it is accessible.